1. Field of the Invention
The present invention relates to a small, automated sewage treatment system to be installed and used in individual residences in lieu of a large-scale municipal sewage treatment plant.
2. Description of the Prior Art
Self-contained subterraneous sewage treatment systems have been mostly used in communities where residences are not connected to a municipal, centralized sewage treatment facility. Most types of subterraneous sewage treatment system comprise a large septic tank whose effluent is discharged directly into a large drain field where pathogens are supposed to breakdown with soil contact. The entire sewage flow is powered by gravity and the tank itself is water tight and usually divided by a baffle into two interconnected compartments. This division allows for improved digestion of waste materials. When the waste enters the septic tank, the heavy solids (primarily feces) sink to the bottom to form a layer of “sludge.” The lighter materials (grease, fats, small food particles, etc.) float to the surface forming a layer of “scum.” Between these two layers is a soup of suspended materials and water soluble chemicals, such as urea from urine and many household chemicals. The baffle between the two chambers has flow ports in the middle, thus allowing only the clarified water in the first compartment to enter the second one. This increases the efficiency of the septic tank at removing suspended solids. The second compartment receives its “load” of liquid mixture, already substantially clarified because most of the solid particles have settled out of the liquid in the first compartment. There also is little turbulence in the second compartment, because the load enters more slowly. Both of these factors allow settling of finer suspended solids in the first compartment.
The typical sources of waste entering a septic tank are toilets (approximately 38%), laundry (25%), showers/baths (22%) and sinks (15%). The principal contaminant of concern is microbiological, such as pathogenic bacteria and viruses from human feces. Phosphorus, a contaminant introduced from many laundry detergents, typically is not a groundwater contamination problem because it is readily taken up by iron, aluminum and calcium naturally occurring in the soil. Urea is converted by the septic tank flora into nitrate and ammonium. Possible metal contaminants include lead (from lead water pipes or lead solder on water pipes), arsenic (found as a contaminant in phosphate detergents), iron, tin, zinc, copper and cadmium. These metals are not typically a concern in septic systems.
The process of digestion in the septic tank is carried out primarily by microbes excreted from our gastrointestinal tracts, such as E. coli, for example. Digestion is an anaerobic process, meaning that oxygen is not required. Gases (hydrogen sulfide and methane) are produced and must be vented. Basically the same thing that happens in a septic tank also occurs in our intestinal tract and in centralized sewage treatment plants. However a properly operating septic tank probably is the most efficient of the three. In the septic tank the gases help stir the sludge, scum and liquid layers which promote further digestion of the solids. A properly functioning tank will convert the bulk of solids into liquid waste through the process of digestion and hence, decomposition.
The liquid faction that leaves the septic tank and enters the drain field is called the effluent. The bacterial level of the effluent is quite high, contrary to popular belief. Typically, the effluent from a septic tank still contains about 70% of the polluted matter in sewage. This effluent is irrigated into the drain field where it slowly percolates through the soil, and in theory pathogen levels are reduced as pathogens break down with soil contact. Bacteria are supposed to eventually die or be removed by the filtering effect of the soil before the effluent reaches the deeper source of drinking water such as an aquifer or spring. In reality, today we know that we can't always rely on “mother nature” to do the disinfecting for us due to the many variables involved in drain field design, operation and maintenance. In places like the Florida Keys, where the substrate consists mostly of porous coral rock with little top soil to slow down and decompose the septic effluent, these systems have significantly contributed to pollution of the surrounding ocean waters. The level of seawater pollution in the Florida Keys has become so critical that Monroe County has installed large air injection pumps at the bottom of the canals in residential areas in order to replenish the oxygen used up by the contaminants introduced into the sea water by conventional septic systems. Oxygen deprived sea water can't support marine life, either plant or animal.
Even in places where soil characteristics are thought be adequate for filtering and bacterial decomposition, there is a significant problem with groundwater contamination as a result of inadequate use and/or maintenance. This contamination is mostly microbiological. Microbes, both bacteria and viruses may remain alive much longer underground than when exposed to the elements above ground. They are small enough that they may travel with the plume of percolating water from the drain field and contaminate drinking water sources, either groundwater or wells.
Lately, new sewage disinfecting systems have been developed to treat the outflow of a septic tank, utilizing ultraviolet light, reverse osmosis membranes, forced oxygenation and/or ozone. All these systems offer effective sewage disinfecting if used within their operating parameters. The problem is that all the state-of-the-art systems available today for disinfection require periodic and professional maintenance, need human intervention for proper daily operation and do not offer an automated fault detection using redundant controllers, one to “operate” and the other to “supervise” and report to central municipal location a malfunctioning “operator.”
In disinfection systems utilizing ultraviolet light disinfection, the light bulbs need to be replaced often and they are very expensive. Also, the bulbs need to be cleaned periodically to remove accumulated sediment or they will lose their effectiveness.
The disadvantages of reverse osmosis membranes, is that these membranes are expensive and they need to be back-flushed periodically or they lose their effectiveness.
Forced oxygenation systems can't guarantee that all the bacteria are killed all the time because of all the variables involved, such as varying ambient temperatures and a continuously fluctuating sewage volume and flow rate.
Ozone gas is a very effective disinfectant and deodorizer but it requires a large amount of electrical power to convert oxygen into ozone.
All of these systems do not offer the long-term reliability and effectiveness associated with professionally maintained municipal sewage treatment plants.
In summary, the long-term effectiveness of existing prior art home sewage treatment systems is compromised by their need for periodic and professional maintenance and they don't offer the level of reliability required for totally unattended operation.
For example, U.S. Pat. No. 3,948,601 to Fraser et al., teaches the use of RF waves to ionize argon into a gas plasma at approximately 100 to 500 C. It also teaches that effective sterilization can be accomplished with “cool plasma” at only 25 to 50 C and very low pressure. However, sterilization by plasma gas does not constitute direct RF sterilization. It also requires a much higher field strength and power consumption than is required for microwave sterilization. Also, because it lacks any type of fault detection and reporting to a central location, it is not suitable for unattended operation.
U.S. Pat. No. 5,162,083 to Forbes, et al., describes an individual home waste water treatment plant conversion apparatus. A method and apparatus for converting a standard anaerobic septic tank system to an aerobic system are disclosed. Disinfection is accomplished by adding chlorine into the effluent, thus making this system unsuitable for unattended applications.
U.S. Pat. No. 5,647,986 to Nawathe, et al., describes an automated wastewater treatment mini-plant intended for installation and use in individual residences. It comprises a settling tank to remove suspended solid, an intermediate tank, where the sewage is aerated and churned, an aerator-clarifier tank, where the effluent undergoes further aerobic treatment without dilution with incoming water, and a disinfecting tank, where a chemical disinfectant such as chlorine is added before dispersion of the treated water into a drain field. The use of a chemical disinfectant requires periodic addition of chlorine to the feed tank, making this system unsuitable for unattended applications, such as in a second home when the owner is away for long periods of time. This patent also describes the use of a microprocessor for automatically operating the system and for detecting and reporting faults to a central location. However, it lacks a mechanism or device for detecting a malfunctioning or an inoperable microprocessor which may render the wastewater treatment unit to function below specifications or inoperable, resulting in unpleasant and potentially serious health hazards for the community.
U.S. Pat. No. 5,697,291 to Burgener, et al., describes a method and apparatus for microwave pasteurization of a continuously flowing food product, such as juice or milk. It teaches careful preheating of the fluid to a temperature a few degrees below that of pasteurization or inactivation temperature coupled with precise temperature regulation during microwave pasteurization to avoid changing the food taste by scorching it. The Burgener method and apparatus are not meant to be used for sewage treatment applications, as they lack all the other elements necessary for proper sewage treatment.
U.S. Pat. No. 6,248,985 to Tomasello, teaches the use of relatively low frequency (11 MHz) RF waves and very high field strength (50 Kilovolts per meter) to heat and disinfect large amounts of medical waste as it is pushed through a large diameter tube (12 inches) by a screw-type extruder. The low frequency RF radiation heats the medical waste to between 90 and 100° C. The teachings of Tomasello are appropriate for large scale disinfection of medical waste where deep penetration by RF radiation is essential. Lower frequency, time-varying electric fields, penetrate deeply and heat objects more evenly. Higher frequency, time-varying microwaves (between 1 and 5 GHz) do not penetrate as deeply but heat more rapidly the cells of microorganisms they radiate, and therefore are more suitable for small scale sewage treatment if the design of the radiation chamber employs a large ratio of pipe length to pipe diameter, as taught by the present invention. Also micro-wave generators, magnetrons, which emit energy in the 1-5 GHZ range are readily available “off the shelf” and are very inexpensive, particularly with respect to radio frequency generators.